The invention relates to a record carrier comprising a disc-shaped substrate with a radiation-sensitive information layer provided with information areas arranged in accordance with a spiral or concentric track pattern. Such a record carrier is intended for recording and/or reproduction of digitally coded information of fixed bit frequency by a beam of radiation.
The invention, furthermore, relates to an apparatus for manufacturing such a record carrier, to an apparatus for recording information thereon, and to an apparatus for reproducing information recorded in the information areas of such a record carrier.
A record carrier of the type mentioned in the preamble as well as apparatus for recording and/or reading information on and/or from such a record carrier is known from Netherlands Patent Application No. 7,802,859, which has been laid open to public inspection and corresponds to pending U.S. application Ser. No. 131,316, filed Apr. 14, 1980. On this record carrier the information areas alternate with synchronization areas in the track direction. The synchronization areas contain the address of an adjacent information segment in which data is to be recorded. In order to obtain a radial tracking signal, i.e. a signal for keeping the laser beam centered on the track, in said application it is is proposed to give the track a radial variation or undulation of a frequency which is low relative to the bit frequency. The radial track variations produce a corresponding modulation in the reflected beam so that a signal indicative of the deviation of the laser beam from the center of the track to be followed can be derived from the detected radiation. One drawback of this construction is that the phase relationship of the detected modulation and the radial track variations must be known in order to determine the direction of the tracking error so that a reference signal is required.